#include <BLEDevice.h>
#include <BLEUtils.h>
#include <BLEServer.h>

#ifndef LED_BUILTIN
#define LED_BUILTIN 15   // XIAO ESP32-C6 user LED (active-LOW)
#endif

#define SERVICE_UUID        "4fafc201-1fb5-459e-8fcc-c5c9c331914b"
#define CHARACTERISTIC_UUID "beb5483e-36e1-4688-b7f5-ea07361b26a8"

// Handle incoming writes from the app
class LEDWriteCallback : public BLECharacteristicCallbacks {
  void onWrite(BLECharacteristic *ch) override {
    // Works whether getValue() is std::string or Arduino String
    String value = String(ch->getValue().c_str());
    if (value.length() == 0) return;

    value.trim();zz
    value.toUpperCase();

    if (value == "ON" || value == "1") {
      digitalWrite(LED_BUILTIN, LOW);   // active-LOW: LOW = ON
    } else if (value == "OFF" || value == "0") {
      digitalWrite(LED_BUILTIN, HIGH);  // HIGH = OFF
    }
  }
};

void setup() {
  pinMode(LED_BUILTIN, OUTPUT);
  digitalWrite(LED_BUILTIN, HIGH); // start OFF (active-LOW LED)

  BLEDevice::init("XIAO_C6_BLE_LED");
  BLEServer  *server  = BLEDevice::createServer();
  BLEService *service = server->createService(SERVICE_UUID);

  BLECharacteristic *ch = service->createCharacteristic(
    CHARACTERISTIC_UUID,
    BLECharacteristic::PROPERTY_READ | BLECharacteristic::PROPERTY_WRITE
  );
  ch->setCallbacks(new LEDWriteCallback());
  ch->setValue("Connected.");

  service->start();

  BLEAdvertising *adv = BLEDevice::getAdvertising();
  adv->start();
}

void loop() { /* nothing needed */ }